Conventionally, the variable geometry turbocharger is known which can improve the performance of the engine over a wide range from a low revolution region to a high revolution region.
Here, a variable geometry turbocharger is disclosed in Patent Document 1.
The above described turbocharger has a configuration in which a turbine housing and a compressor housing are integrally connected via a bearing housing, and a turbine impeller disposed inside the turbine housing and a compressor impeller disposed inside the compressor housing are connected by a rotating shaft that is disposed so as to be rotatable inside the bearing housing.
An exhaust gas inlet port is disposed at the turbine housing, and the exhaust gas that flows in from the inlet port is introduced in a turbine scroll flow path inside the turbine housing. A variable nozzle unit (an exhaust nozzle) is disposed at the turbine housing side of the bearing housing, wherein the variable nozzle unit guides the exhaust gas introduced in the turbine scroll flow path to the turbine impeller and can change the flow rate thereof.
The variable nozzle unit includes a shroud ring that is an exhaust inlet wall of the turbine housing side and a nozzle ring that is an exhaust inlet wall of the bearing housing side. The nozzle ring and the shroud ring are connected with a predetermined gap. A plurality of nozzle vanes is disposed annularly between the nozzle ring and the shroud ring in order to adjust the flow rate of the exhaust gas.
A predetermined gap is provided between the shroud ring of the variable nozzle unit and the turbine housing. Although the gap is not required intrinsically, since thermal deformation occurs between when the turbine housing is cooled and when the turbine housing is heated, their positional relationship relative to the shroud ring change. Therefore, the gap is provided.
However, the exhaust gas inside the turbine scroll flow path leaks to an outlet side of the turbine housing through the gap and turbine efficiency of the turbocharger is decreased. A C-ring for sealing is disposed between substantially cylindrical outer circumferential surface of an extension section that is extended from an inner circumferential edge of the shroud ring to the turbine housing and an inner circumferential surface of the turbine housing facing the outer circumferential surface of the extension section to block the gap. The C-ring is formed of an elastic body and can follow the thermal deformation of the turbine housing due to the elastic force thereof.